1. Field of the Invention
The present invention relates to active-matrix-type liquid crystal displays using a lateral-direction-electric-field mode (in-plane-switching, referred to as IPS in the following explanations), and to a manufacturing method for the displays.
2. Description of the Related Art
Recently, the IPS mode, by which an electric field is applied to a liquid crystal parallel to its substrate, has been used in active-matrix-type liquid crystal displays, as a method for obtaining super wide viewing angle. When the IPS mode is adopted, it has been proved that variation in contrast and reversal of gradation level rarely occur (for example, refer to Patent Document 1).
FIG. 9 (a) is a plane view illustrating a pixel portion of a liquid crystal display using a conventional general-use IPS mode, and FIG. 9 (b) is a cross-sectional view along the line “A-A” of the pixel portion. The liquid crystal display includes a TFT array substrate “100”, a facing substrate “200”, and a liquid crystal “300” installed between the substrates. The TFT array substrate 100 includes: gate lines “1” as a plurality of scan signal lines formed on a transparent-insulation substrate “92” such as a glass substrate; a common line “3” for forming storage capacitance; a plurality of source lines “2”, for applying a signal voltage, that cross the common line 3, over an intervening gate insulation film “8”; a plurality of pectinate pixel electrodes “5” formed parallel to the source lines 2; a plurality of pectinate common electrodes “6” arranged alternately with and parallel to the pixel electrodes 5; a semiconductor film “7” forming switching elements each composed of a thin film transistor (referred to as a TFT in the following explanations); drain electrodes “4”, source electrodes “91”; and an interlayer insulation film “9”.
When a different signal voltage from another pixel is supplied to the source lines 2 in a state in which a switching element is off and a voltage for driving the liquid crystal 300 is retained by the storage capacitance between the pixel electrodes 5 and the common electrodes 6, a leak electric field is generated from the source lines 2 by the signal voltage, which varies the molecule alignment state of the liquid crystal 300 neighboring the source lines 2. Thereby, wrong display, such as cross-talk, has been caused in the source line 2 directions. In the conventional liquid crystal display, in order to reduce influence to images in the region where the molecule alignment of the liquid crystal 300 is disturbed, and in order for the common electrodes 6 neighboring the source lines 2 to serve also as electric-field-shielding electrodes, portions of the common electrodes 6 neighboring the source lines 2 are wider than the other portions. As a result, there have been problems in that the width “L1” of a region, near the source lines 2, that does not contribute to light transmission is expanded, so that a pixel aperture rate is decreased.
In order to solve the above-described problems, a configuration illustrated in FIGS. 10 (a) and (b) has been proposed. FIG. 10 (a) is a plane view illustrating a pixel portion of a liquid crystal display using the IPS mode, and FIG. 10 (b) is a cross-sectional view along the line “B-B” of the pixel portion. The pixel electrodes 5 and the common electrodes 6 are formed on the interlayer insulation film 9 in the configuration. By etching the gate insulation film 8 and the interlayer insulation film 9 in the same processing step, contact holes 10 for electrically connecting the common line 3 and the common electrodes 6 as well as the drain electrodes 4 and the pixel electrodes 5 are formed. The common electrodes 6 are arranged to cover the source lines 2 so that both of these overlap each other.
In the above configuration, because the common electrodes 6 neighboring the source lines 2 have a function as electric-field-shielding electrodes and effectively shield a leak electric field generated from the source lines 2, the molecule misalignment state of the liquid crystal 300 can be reduced. Thereby, a width “L2” that limits light transmission can be narrowed, and the pixel aperture rate can be increased (for example, refer to Patent Document 2).
Patent Document 1:
    Japanese Laid-Open Open Patent Publications 1996-254712Patent Document 2:    Japanese Laid-Open Open Patent Publications 2003-307741